Various types of hand tools have been designed which operate on the basis of a lever action, the lever being arranged so that the force applied to the cutting blades increases as the shears are closed. Typical of this type of cutting device are U.S. Pat. No. 1,436,603, issued on Nov. 21, 1922, for Pruning Device; U.S. Pat. No. 2,744,323, issued on May 8, 1956, for Shears; U.S. Pat. No. 2,766,526, issued on Oct. 16, 1956, for Metal Shears; U.S. Pat. No. 2,528,816, issued on Nov. 7, 1950, for Hedge Shears; and U.S. Pat. No. 787,414, issued on Apr. 18, 1905, for Pliers. Each of these devices use a connecting link to achieve a mechanical advantage by increasing the force applied as the shears are closed. The patent to Walton 787,414 discloses a pliers which provides a cutting force that increases rapidly from zero and decreases rapidly to zero as the arm pivots to a right angle.
The patents to Krivec 5,245,755, issued on Sep. 21, 1993, for Force-Multiplying Mechanism, and Hexdall 3,587,173, issued on Jun. 28, 1971, for Metal-Cutting Shears, both provide a lever action which provides an increasing force as the shears close for cutting metal.